The present invention relates to a method for the formation of a film. More particularly, the invention relates to a silica film which has a dielectric constant as low as 2.2 or below and excellent mechanical strength and is useful as a dielectric film in semiconductor devices, etc.
Silica (SiO2) films formed by vacuum processes such as CVD have hitherto been used frequently as dielectric films in semiconductor devices and other devices. In recent years, a dielectric film formed from a coating fluid has come to be used for the purpose of forming a more even dielectric film. This film, which is called an SOG (spin on glass) film, comprises a tetraalkoxysilane hydrolyzate as the main component. Furthermore, as a result of the trend toward higher density integration in semiconductor devices and the like, a dielectric film called an organic SOG film has been developed which comprises a polyorganosiloxane as the main component and has a low dielectric constant.
However, with further progress in the high density integration or multilayer interconnetion in semiconductor devices and the like, a dielectric film having a lower dielectric constant and excellent mechanical strength has come to be desired.
Japanese Patent Laid-Open No. 6-181201 discloses an insulating film having a lower dielectric constant for use as a dielectric film. This insulating film is intended to be provided as an insulating film for semiconductor devices which has reduced water absorption properties and excellent cracking resistance. It comprises as the main component an oligomer having a number-average molecular weight of 500 or higher obtained by condensation-polymerizing an organometallic compound containing at least one element selected from titanium, zirconium, niobium, and tantalum with an organosilicon compound having at least one alkoxy group in the molecule.
This insulating film of the related art, however, has a dielectric constant of 2.5 or higher and is hence still insufficient for application to semiconductor devices operating at high frequency. A coating film having an even lower dielectric constant is desired.
Accordingly, the present invention provides a method for the formation of a film for eliminating the problem described above. More particularly, the present invention provides a method for the formation of a silica film which has excellent mechanical strength showing a dielectric constant of generally 2.2 or lower, preferably 2.0 or lower, more preferably 1.9 or lower, and hence is useful as a dielectric film in semiconductor devices and the like.
One object of the present invention is to provide a method for the formation of a silica film which comprises treating a film in a supercritical medium, the film comprising (A) a siloxane compound and (B) at least one member selected from the group consisting of (B-1) a compound compatible with or dispersible in ingredient (A) and having a boiling or decomposition temperature of from 150 to 500xc2x0 C. and (B-2) a surfactant.
Another object of the present invention is to provide a silica film obtained by the above method for the formation.
Still another object of the present invention is to provide a low-dielectric film comprising the silica film.
Further object of the present invention is to provide a semiconductor device using the low-dielectric film.